Amplifying circuits comprising a plurality of amplification stages in cascade



July 24, 1951 ROGERS 2,561,597

AMPLIFYING CIRCUITS COMPRISING A PLURALITY OF AMPLIFICATION STAGES IN CASCADE Filed Feb. 13, 1948 2 Sheets-Sheet l 4a as 46 k AMPLIFIER ou'mn AMPLIFIER 7 as f 45 INVENTOR.

ALFRED A. ROGERS BY AG NT July 24, 1951 A, A. ROGERS AMPLIFYING cmcuus COMPRISING A PLURALITY 0F AMPLIFICATION STAGES IN CASCADE 2" Sheets-Sheet 2 Filed Feb. 15, 1948 I? 6 7 0. I. .3 15 i T m n. H 4 .H 5 u L 3 P P M M A A u u v .r H In u 1 T 4 U L" k 4 W FIG.|

JNVENTOR. ALFRED A. ROGERS BY AGE T .cating instrument, e. g. a galvanometer.

Patented July 24, 1951 UNITED STATES Pix-TENT orriscs AMPLIEYING-CIRCUITS COMPRISINGAPLU- RALITY or AMrLmroA'moN STAGES IN- CASCADE Alfred A. Rogers, Chicago; 111." Application February 13, 1948, Serial No... 8,079]

flee to produce an output voltage great enough to'operate properly a conventional simple irdi- A ditionalamplification is required and'it is a further object of this invention to carry out such additional amplification in such a manner that, when direct current is to be amplified, the polarity of the direct current applied to the input of the balanced stage will be preserved so that this polarity will appear at the output of the amplification stage or stages followingv the balanced input stage. The additional amplification may be brought about by the use of amplification is used for amplifyingd'irect current, the polarity of the direct current applied to the input of the balanced input stage will be preserved so that this polarity will appear at the combined output of the two conventional amplifier systems.

It is a further object of the invention to provide an amplifying circuit having at least two balanced stages" of' amplification each comprising two tubes or two sets of tubes in bridge arrangement and two amplifier systems, one for each tube or setof tubes of the last balanced stage of amplification, having their outputs arranged. in bucking relationship.

Still a further object of the invention is to provide an amplifying circuit having at least two balanced stages of amplification each comprising two tubes or two sets of tubes in bridge I arrangement and two amplifier systems constages which arev either themselves: balanced stages or are conventional amplifier systems.

Whether direct or alternating currentisto be amplified in the circuit, the plate supply of the balanced amplification stages is alternating current.

A further object of this invention is, to provide an amplifying circuit comprising a plurality of balanced stages of amplification, any two subsequent stages having plate supplies differing in phase by 180. 7

It is a further object of the. invention to providean amplifying circuit comprising a plurality oi balanced stages of amplification, any two subsequent stageshaving plate supplies differing in phase by L809, wherein means are provided to store a portion of the output voltage of the respective preceding balanced stageso. that when the respective subsequent balanced stage becomes conductive, at which time said preceding balanced stage has. become non-conductive, voltage is nected in parallel to the plates of the two tubes or sets of tubes of the last balanced stage with an electric valve preceding each amplifier system so that the output of the balanced system goes either into the one of the two amplifier systems or into the other, depending on the polarity of the current appliedto. the input of the firstbalanced stage.

Other objects of the invention will appear as the descriptionproceeds, reference being bad to the accompanying drawings in which:

Fig. 1 shows a circuit comprising four balanced stages of amplification, the output of each tube of the last balanced stage being connected to one of two. amplifier systems; and

Fig. 2' shows the plates of the two tubes of the last balanced stage of amplification connected in parallel with both of two amplifiers.

Fig. 1 shows a circuit. wherein four balanced or bridge stages are used, but any other number of balanced stages, such as two or three or more than four, may be used. The four balanced systems of Fig. l are generally indicated by the reference letters A, B, C and D. The first balanced stage A comprises two amplifier tubes I0 and H arranged in parallel. Tube to has a cathode. I2, a plate It and between said cathode and plate at least a control grid l4, and tube ll likewise comprises a cathode IS, a plate l6, and between these two. electrodes l5, H5 at least one grid l1. Plate 13 of tube I0 is connected through a load impedance 20 to the one line 18 of a supply of alternating current of any suitable wave shape which may be derived from any suitable source, such as the commercial line supply, a vacuum tube oscillator or some other generator or alternatingcurrenti In parallel to plate I3, plate I6 ing to tube |l.

3 of tube H is connected to said supply line l8 by means of a load impedance 2|. Cathode impedances 22 and 23 connect, respectively, the oathodes I2 and of the two tubes Ill and II to the adjustable by a slide arm as conventional with potentiometers. 25 and 26 denote grid resistors for the two control grids l4 and I1, and 21 and 28 are terminals to which an external voltage to be amplified in the circuit may be applied. The terminals 21, 28 may be shunted by a condenser 29 in order to reduce the pick-up of stray'fields.

The tubes H3, II are of identical nature and the plate impedance, the cathode impedance and the grid resistor belonging to tube It! have the same sizes as the corresponding elements belong- Thus a bridge circuit is formed wherein the two tubes It, H in series with the cathode impedances 22, 23 form the one pair of bridge arms and the plate impedances 2E3, zl'the two other bridge arms. As long as no external voltage is applied to the grids l4 and H or to one of these grids, the bridge is balanced and there is no potential difference between point 39 connected to the plate of the tube iii and point 3| connected to the plate of the tube H, the voltage drops across the plate impedances 2t and 2| being equal.

When an external voltage is applied to either grid M or I! or both, by'connecting this external voltage either between one of the supply lines '|8, l9 and one of the terminals 21, 23 or between these two terminals 21, 23, the balanced condition described will no longer exist. Assuming that the external voltage be applied between the grids i4 and H and be of such polarity as to make the grid M of tube Ill more positive than thegrid H of tube N, then point 3|] will be more I positive than point 3| and the potential difierence arising between the points to and 3| will be proportional to, and larger than, the applied external voltage and of definite direction. If the polarity of the external voltage changes, so that the grid becomes more positive than the grid M, then of the two points 3i! and 3| the latter becomes more positive and there will exist a potential difference in the direction from 3| towards 3B, opposite to what it was before. The

magnitude of the potential difference between the points 3| and 30 is again proportional to, but larger than, the magnitude of the external voltage.

The intermediate stages B and C are constructed similarly to the stage A except that the input terminals 2'| and 28 and the grid resistors 25 and 28 are omitted. The final stage D is similar to the intermediate stages B and C but has output terminals 50 and 5| between the cathodes and the cathode impedances of the two tubes of the stage. Those parts of the stages B, C and D which correspond to parts of the stage A are denoted by reference numerals corresponding with those which are used for the stage A but followed by indices 2 and 3 for the stages B, C and D, respectively.

All the balanced stages A, B, C, D are supplied with alternating current through the leads i8 and D to these leads is so that eachtwo consecutive stages operate with a phase difierence of The plates of the tubes It and II of the stage A and of the tubes I02 and i IQ of the stage C are connected to the line l8, whereas the cathodes of these tubes l0, Hi2 and H2 are connected to the line I9. Of the tubes W1 and N1 of the stage B and its and H3 of the stage C, the cathodesare connected to the line I8 and the plates to the line I9.

The grids of each consecutive stage are directly coupled with the corresponding plates of the respective preceding stage. However, across the grids of the two tubes of each of the stages B, C and D there is arranged a common storage condenser, the condenser for the stage B being indicated at E01, that for the stage C at 6th, and that for the stage D, at (563. Each of the stages A, B, C and D will conduct current only through onehalf of each cycle of the alternating current carried by" the supply lines l8, l9. In particular, the stages A and C will be conductive during the one half cycle and the stages B and D during the other half'cycle of the alternating current. Considering now thetwo stages A and B, it-will be apparent that these two stages will be operative only alternatively, which is to say, that stage B will become conductive only after the preceding stage A has reached the end of its conductive half-cycle and will remain so conductive for half a cycle during which period the stage A is non-conductive. After that, stage A becomes again conductive and stage B nonconductive. Thus, the two stages A and Bare never operative at the same instance and consequently these two stages are efiectively electrically sepaportion of the output of the stage A while the latter is in its conductive phase and will impress a voltage upon the grid circuits of the stage 33 during the next half cycle when the stage A has ceased to be conductive. What has been said in regard to the stages A and B applies to the relationship of the stages B and C and'also of the stages C and D so that any two consecutive stages are separated from each other, being at a phase difference of 180 relative to the preceding as well as to the following stage. I

All the four bridge stages A, B, C and D are inbalanced 'conditionas long as no external voltage is applied to either grid I4, H or to both these grids of the bridge stage A and no potential difference will exist at the end points 393 and 3 is of the load impedances 293 and 2h, since the voltage drops across the load impedances are of equal magnitude. If an external voltage is applied to the grid or grids of the balanced system A this will cause an unbalance so that one of the points 30, 3| will become more positive than the other, resultingin a potential diilerence of definite direction between these points 36 and 3|. This potential difference, which again is proportional to, and larger than, the applied external voltage, is carried through the three further bridge stages B, C and D, undergoing a further amplification in each of those stages. The points 303, 3|: and 323 of the last balanced stage D are shown connected to terminals'SB', 4|, 3'? and All so that connection may be established'with the input terminals 36, 4|, 3'1 and 40 of a pair of similar amplifier systems 34 and 35 of conventional design having identical gains.

the amplifying system 34 will ages.

s The two amplifier systems 34, 35 have their own power supply system or systems supplying the, tubeswith direct current. 36 and 3'! are input terminals and 33 and 39 exit terminals of the amplifier system 34, whereas 40 and 4! denote input terminals, and 42 and 43 exit terminals of the amplifier system 35. The voltage appearing across the load impedance 203 is impressed upon the amplifier system 34 by means of the point 303 being connected to the terminal 3t and the point 323 to the terminal 3?, whereas the voltage across the load impedance 2H3 is'impressed upon the amplifier system 35 by means of the input terminals 40, 4| of this amplifier system being connected to the ends 323 and N3 of the load, impedance 213. The exit terminal 33 or the amplifier system 34 is connected" to the exit terminal 43 of the amplifier system 35 and the respective other exit terminals 38 and 42 0fthe two amplifier systems are connectedto twojouter terminals 44 and 35, each through a rectifier 4t and 41,, respectively. Thus the outputs of the two amplifier systems 34 and 35 are connected in bucking relationship to each other. s

When no external voltage is applied to the control grid of one of the tubes l0, H or to the control grids of both said tubes l0, ll of stage A, then, due to the powersupplied to the tubes through the lines l8, [9, both loadimpedances 26 and 21 and each of the two amplifying systems 34 and 35 will be impressed with input voltages of identical magnitude. Therefore, the voltage appearing at the exit terminals 38, 33 of be the same as the voltage between the exit terminals 42, 43 of the amplifying system35 and on account of the bucking connection between the exits of the two amplifying systems the voltage difference appearingat the output terminals 44 and 45 will be zero. If, however, an external voltage is applied to the controlgrid or grids of the tubes 10, ll of the first balanced amplification stage A, the voltage developed across the load impedance 203 will be diife'rent from-the voltage across the load impedance 313, so that the two amplifying systems 34 and 35 will have dififerent input volt- Consequently, a voltage will appear at the output terminals 44 and 45 and this voltage is proportional to the diiT-erence of the voltages across the load impedances 203 and Us. If the external voltage applied to the control grid or grids of the tubes [0, II is D. C., then the potential difference between the output terminals 44 and 45 is of definite direction depending on the'polarity of said applied external voltage.

When this polarity changes, the direction of the potential difference at the output terminals 44, ochanges correspondingly. Thus, all changes in the magnitude and/or polarity of the applied external voltage are transmitted from the input of the balanced amplification stage all the way through to the output terminals 44, 45 under maintenance of a zero axis throughout.

The pair of amplifier systems 34 and 35, instead of being connected to the balanced stages A to Din the manner shownin Fig. 1, may be connected in the manner shown in Fig. 2, in which latter figure of the four balanced stages A to D there is shown only the last stage D. Point 303 at the plate endof the load impedance 203 is connected in parallel with the input terminal 36 of the amplifier system 34 and with the input terminal 43 of the amplifier system 35, in. each of these two parallel connections therebeing in- .:ent .ul -j oi t 3 m scien e i .1; ise connected in p allel to; not; amplifier s st ms a and the some t on to the mpl 'fiqt s stem. 34' b ng a the i inut term nals a dyt e ommun sm? s s em 35 atthe n ut el: cal. 41-. 1 Where s n the lr u t wil e-Q the. ol ages t m ed nqes. 0a an 1 e e ch a p is fl d s parately heme vcl ag f a the. m l fie system i the oth r volta in the ampli ier sy 3.5 the ci quit at F g 2 hi t e diifee ence of the two voltages across the impedance's 2113. 2 3 h qh amp fi d theme a plifier y ems and, 35- D pe ing o whet er t e a e 3 r t ate s v o tage differe esbet en he P i ts 311 a d 31 p ss s ei he hro gh e ve 48 o the a e t I 48 is he a v Perm tin the Passa e o s i e c rr n s and. S the. i l i adm t n n ga i e: rrents t em, ince" c t l in? pu to th m lifi r sy t m. 345 an -49 t e in u o e ampl fie syst m 353 he resul ng diff ential voltage be een thepqint n a d 3| will be d ce hr h he. v lve 48 o the am: plifier system 34 if the plate I33 of tube I03, is

relatively more'positive, but throughthe. valve ,49-into the amplifier system 35. if the plate I63 of the tube I l s m Posi v Sinc in i arrangement always only one of the two amplifier systems 34 3:; is operative at any instant, the exit terminals 33, 39, 42 and 43 may be connected with each terminals 44 and 45; either in the bucking manner as shown in Fig 1 or, as shown in Fig. 2, an adding series connection may be. used. In either case the voltage appearing at the output termials 44. 45 is a P QPQ tiQnamu t le o the 1 1 balancing external voltage appliedftoi'the grid of one of the tubes Ill, H of the first balanced amplifi t o tag to he QQ FITQIQTMS of both. sa d u s h po a y o th s vol a e ap ea ing at the output terminals 44, 4'5 changes ae-; cording to the polarity'changes or the unbalane ins v lt ge f Whereas in Figs. land 2 as described thus far'the output voltage has been obtained from the plate circuit includ'i g the plate imp'edances 2D and 2!, theoutput. voltage may be taken. from the cathode circuit n which case "the voltage drops across the cathode impedances 223 and 233 are subtracted from each other. If the output is so taken from the I put results than if the output is taken from the. plate circuit; The pointjfl may be connected to a terminal 33" and the point 5| to a terminal 41"whereas the center point 53 may be connected to two terminals 31" and 43""to enable again the connection to the input terminals 36; 4| 3'1 and 40 ofthe two amplifier systems 34 and 35. l 1

Where the amplification obtainab e b the cascade of the balanced stages A, B, C, D isfsuflicient to transform the minute external voltage pp ied o he p t o he fi t teele A i toa e a tor r h shl q tp ltae neith po n 0 a d '3 or he Poi 53 and 51, th n e e n t a d qllllsft rlfll lelfi at" s more o itive. t e esu tin oth r and ith t e u p t cathode circuit such as at the terminals 53 andiil, a lower impedance out- 41' connecte therewith) or' so and, s1 (or the terminals 3 6".anjd 4|" connected therewith) may be'used directly as output terminals, dispensing with the two amplifier systems 34 and 35;

While I have shown in the drawing two particular embodiments of -my'invention', I desire it to beunderstood that these pa rticular embodi: ments' havebeen given byway of example only and that various modifications and re-arrangements of the details of thecircuits shown may be made without departing from the spirit, of the invention 'o'rlthe scope offth'e appended claims; For example, while triodes are shown in the draw-- ings, tubes with a plurality of grids, e. g. pentodes, may. be used;' Or, while each of the balanced stages is shown as comprising two tubes in paral lel, therev may be several tubes connected in series for each of the tubes shown in the drawing, etc.

WhatIclaimis:

1'. An amplifying circuit comprising a plurality of balanced bridge circuitsin cascada'two of the bridge arms of each of said bridge circuits in cluding each at least one amplifier tube having a' cathodaa plate and at least a, control grid and the other two bridge arms of each of said bridge circuits including each a load impedance for one of said two amplifier tubes, terminals connected with the grid circuit of a tleast one of said tubes of the (first of said bridge circuits in cascade for the'application of an unbalancing external voltage, a source of alternating current for supplying power to the discharge paths across said tubes of said bridge circuits of the cascade, the power supplies to the tubes of any bridge circuit being of the same phase and the power supplies to the tubes of any two subsequent bridge circuits differing in phase by 180, and a storage condenser so arranged as to be common as a connection between either of the output electrodes ef the two balanced tubes of any preceding bridge circuit and oneof the input gridsof the two balanced tubes of the respective subsequent bridge circuit. 4

e 2. An amplifying circuit comprising a plurality of, balanced bridge circuits in cascade, two of the bridge arms of each of said bridge circuits including each at least one amplifier tube having a cathode, aplate and at least a control grid and the other two bridge arms of each of said bridge circuits including each a load impedance for said amplifier tubes, terminals connected with the grid circuit of at least one of said tubes of the first of said bridge circuits in cascade for the application of an unbalancing external voltage, a source of. alternating current for supplying power to the discharge paths across said tubes of said bridge circuits of the cascade, the power supplies to the tubes of any bridge circuit being of the same phase and the power supplies to the tubes of any two subsequent bridge circuits differing in phase by 180, a storage condenser so arranged as to be common as a connection between either of the output electrodes of the. two balanced tubes of any preceding bridge circuit and oneof the input grids of the two balanced tubes of the respective subsequent bridge circuit, a pair of additional amplifier systems having identical gains, said two additional amplifier systems being connected in parallel to the output of the last of said bridge circuits in cascade so as to derive from the. last named bridge circuit the. difference of the voltages created across the'load impedances for said two amplifier tubes of that last named bridge circuit, an electric valve'preceding each of said two addi tional amplifier "systems, said two valves being ls-arse;

arranged to be operative in opposite directions so that one of said two valves allows the. passage of current of one polarity only and the other valve the passage of current of the opposite polarity only and thus the output of the last of said bridge circuits is delivered either into the one of said two additional amplifier systems or into the other, depending on the polarity of the said unbalancing external voltage applied to the grid-circuit or circuits of said first of said bridge circuits in cascade.

3. An amplifying circuit comprising a plurality of balanced bridge circuits in cascade, two of the bridge arms of each of said bridge circuits including each at least one amplifier tube having a cathode, a plate and at least a control grid and a cathode impedance in series with said cathode, and the other two bridge arms of each of said bridge circuits including each a plate impedance for said amplifier tubes, terminals connected with the grid circuit of at least one of said tubes of the first of said bridge circuits in cascade for the application of an unbalancing external voltage, a source of alternating current for supplying power to the discharge paths across saidtubes of said bridge circuits of the cascade, the power supplies to the tubes of any bridge circuit being of the same phase and the power supplies to the tubes of any two subsequent bridge circuits differing in phase by a storage condenser so arranged as to becomrnon as a connection between either of the output electrodes of the two balanced tubes of any preceding bridge circuit and one of the input grids of the two balanced tubes of the respective suband the other two bridge arms of each of said bridge circuits including each a plate impedance for said amplifier tubes, terminals connected with the "grid'i'circuit of atleast one of said tubes of the f rst of said bridge circuits in cascade for the application of an unbalancingexternal voltage, a source of alternating current for supplying power to the discharge paths across said tubes ofsaid bridge circuits of the cascade, the power supply to'the tubes of any bridge circuit being of the same phase and the power supplies to the tubes of any two subsequent bridge circuits differing,

in phase by 180", a storage condenser so arranged as tdbe'common as a connection between either of the output electrodes of the two balanced tubes of any preceding bridge circuit and one of the input grids of the two balanced tubes of the respective subsequent bridge circuit, two output terminals each connected between the cathode of one of said tubes of thelast ofisaid bridge cir v cuits 1 in cascade and its coordinated cathode impedance, a pair of additional amplifier systems for further amplifying the amplified voltage appearing at said output terminals, said pair ofadditional amplifier systems having a common output and being joined to said output terminals of said last of said balanced bridge circuits so [as to preserve the polarity of said unbalancing external voltage beyond said first of said bridge circuits in cascade all the way through said pair of additional amplifier systems and in the common output of said pair of amplifier systems.

5. An amplifying circuit comprising a plurality of balanced bridge circuits in cascade, two of the bridge arms of each of said bridge circuits including each at least one amplifier tube having a cathode, a plate and at least a control grid and a cathode impedance in series with said cathode, and the other two bridge arms of each of said bridge circuits including each a plate impedance for said amplifier tubes, terminals connected with the grid circuit of at least one of said tubes of the first of said bridge circuits in cascade for the application of an unbalancing external voltage, a source of alternating current for supplying power to the discharge paths across said tubes of said bridge circuits of the cascade, the power supply to the tubes of any bridge circuit being of the same phase and the power supplies to the tubes of any two subsequent bridge circuits differing in phase by 180, a storage condenser so arranged as to be common as a connection between either of the output electrodes of the two balanced tubes of any preceding bridge circuit and one of the input grids of the two balanced tubes of the respective subsequent bridge circuit, two output terminals each connected between the cathode of one of said tubes of the last of said bridge circuits in cascade and its coordinated cathode impedance, a pair of additional amplifier systems having identical gains, said pair of additional amplifier systems being connected to said two output terminals so that the one of said pair of amplifier systems receives the voltage developed across the cathode impedance for the one of said two amplifier tubes of said last of said bridge circuits in cascade and the other of said pair of amplifier systems the voltage developed across the cathode impedance for the other of said two amplifier tubes.

6. An amplifying circuit comprising a plurality of balanced bridge circuits in cascade, two of the bridge arms of each of said bridge circuits including each at least one amplifier tube having a cathode, a plate and at least a control grid and a cathode impedance in series with said cathode, and the other two bridge arms of each of said bridge circuits including each a plate impedance for said amplifier tubes, terminals connected with the grid circuit of at least one of said tubes of the first of said bridge circuits in cascade for the application of an unbalancing external voltage, a source of alternating current for supplying power to the discharge paths across said tubes of said bridge circuits of the cascade, the power supply to the tubes of any bridge circuit being of the same phase and the power supplies to the tubes of any two subsequent bridge circuits differing in phase by a storage condenser so arranged as to be common as a connection between either of the output electrodes of the two balanced tubes of any preceding bridge circuit and one of the input grids of the two balanced tubes of the respective subsequent bridge circuit, two output terminals each connected between the cathode of one of said tubes of the last of said bridge circuits in cascade and its coordinated cathode impedance, a pair of additional amplifier systems having identical gains, said two additional amplifier systems being connected in parallel to said two output terminals so as to derive from said last of said bridge circuits in cascade the difference of the voltages created across the cathode impedances for said two amplifier tubes of that last named bridge circuit, an electric valve preceding each of said two additional amplifier systems, said two valves being arranged to be operative in opposite directions so that one of said two valves allows the passage of current of one polarity only and the other valve the passage of current of the opposite polarity only and thus the output of the last of said bridge circuits is delivered either into the one of said two additional amplifier systems or into the other depending on the polarity of the said unbalancing external voltage applied to the grid circuits or circuits of said first of said bridge circuits in cascade.

ALFRED A. ROGERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,085,488 Woodward et al. June :29, 1937 2,403,955 Schlesinger July 16, 1946 2,432,826 Smith Dec. 26, 1947 2,434,822 Van Beuren et a1. Jan. 20, 1948 2,436,741 Bussey Feb. 24, 1948 

